1. Technical Field
The disclosure relates in general to a driving method for a liquid crystal panel and a liquid crystal display (LCD), and more particularly to a liquid crystal panel with high display quality and a driving method for such LCD.
2. Related Art
A response time of liquid crystal molecules has much to do with a cross voltage at two ends of the liquid crystal molecules. Therefore, in order to increase the response rate of liquid crystal molecules, an overdriving technology is adopted to increase the response rate of liquid crystal molecules. An overdriving circuit is normally disposed near the liquid crystal panel. However, if a frame rate control (FRC) circuit is disposed before the overdriving circuit, the same gray level value will correspond to different pixel data on different image frames when a static image frame is inputted. This is because after a conversion procedure of frame rate control is applied to the pixel data, an error occurs due to data bit conversion (for example, 6-bit pixel data is converted to 8-bit pixel data) when the pixel data is processed in the overdriving circuit resulting in severe FRC noise.
Generally speaking, the overdriving circuit is implemented by a look up table. Referring to FIG. 1A, an overdriving look up table known to the inventors is shown. In a known LCD, an overdriving unit obtains overdriving pixel data from an overdriving look up table to drive corresponding pixels of a liquid crystal panel according to a boundary value and previous boundary value. The boundary value and the previous boundary value are obtained from the overdriving look up table. The boundary value corresponds to a current image frame. The previous boundary value corresponds to a previous image frame. When the boundary value is equal to the previous boundary value (the dotted area of FIG. 1A), the overdriving unit directly outputs the current image frame without adopting the overdriving technology.
Referring to FIG. 1B, a block diagram of the known LCD is shown. The LCD 100 includes a liquid crystal panel 105, a scan driving unit 110, a frame rate control (FRC) unit 120, a mapping unit 130, the buffer 140, an overdriving unit 150, a processing unit 160 and a data driving unit 170. The liquid crystal panel 105 has several pixels controlled by the scan driving unit 110.
The frame rate control unit 120 converts M-bit pixel data DI—M into N-bit FRC pixel data DFRC—N according to a conversion procedure of frame rate control, wherein M and N are positive integers, and M is larger than N. For example, the M-bit pixel data DI—M is a gray level value 25 corresponding to a static image frame, the N-bit FRC pixel data DFRC—N is one of the gray level values 7, 6, 6 and 6 corresponding to the dynamic image frame. The mapping unit 130 converts the FRC pixel data DFRC—N into a boundary value according to a boundary look up table (not shown). The buffer 140 stores the boundary value.
The overdriving unit 150 is coupled to the mapping unit 130 and the buffer 140 for obtaining a pixel data offset from the overdriving look up table (shown in FIG. 1A) (OD LUT) according to the boundary value and a previous boundary value. The processing unit 160 is coupled to the frame rate control unit 120 and the overdriving unit 150 for obtaining overdriving pixel data by adding the pixel data offset and the FRC pixel data. The data driving unit 170 drives corresponding pixels of the liquid crystal panel 105 according to the overdriving pixel data.
However, at the boundary of the range of the gray level value corresponding to the boundary value, after the frame rate control unit 120 converts the pixel data into FRC pixel data, the FRC pixel data may be changed and the previous boundary value (the dashed area of FIG. 1) will be changed accordingly. For example, if the FRC pixel data DFRC—N is a gray level value 6, the mapping unit 130 converts the gray level value 6 into a boundary value 6. If the FRC pixel data DFRC—N is a gray level value 7, the mapping unit 130 converts the gray level value 7 into a boundary value 13. Thus, for a gray level value 25 corresponding to the unchanged static image frame, if the FRC pixel data DFRC—N sequentially is gray level values 6 and 7, then the overdriving unit 150 obtains a pixel data offset (such as 2) according to the previous boundary value 6 and the boundary value 13. The processing unit 160 obtains the overdriving pixel data 9 according to the pixel data offset 2 and the FRC pixel data 7. However, the static image frame does not change. That is, the overdriving unit 150 generates errors and adopts the overdriving technology according to the boundary value and the changed previous boundary value, such that the liquid crystal panel 105 does not display the correct image.
To resolve the above problem, when the boundary value and the previous boundary value correspond to the areas besides diagonal lines of the overdriving look up table (that is, the dashed area of FIG. 1A), the overdriving technology is not adopted. However, despite that the problem associated with the frame rate control unit 120 is resolved, the overall display quality of the LCD adopting the overdriving technology decreases, and hardware resources are not fully utilized.